Oscillation generating system



April 25, 1939. A. SENAUKE 2,156,230

OSCILLATION GENERATING SYSTEM Filed Oct. 14, 1936 2 Sheets-Sheet l FIG. 1 20 INVENTOR.

ALEXA/V0512 JEN/wk: W I ATTORNEY.

April 25, 1939. SENAUKE 2,156,230

OSCILLATION GENERATING SYSTEM FiledOct. 14, 1956 2 Sheets-Sheet 2 FIG.3

IN VEN TOR. ALEXANDER 5 NA UKE BY ATTORNEY.

Patented Apr. 25, 1939 UNITED STATES PATENT OFFXQE- OSCILLATION GENERATING SYSTEM Application October 14,

Claims.

This invention relates to apparatus for generating and utilizing electrical oscillatory energy, and more particularly so -called ultra-short waves, or ultra-high frequencies.

The invention herein disclosed is of particular value and utility in the therapeutic field, as in so-called high frequency diathermy machines, but as will be readily understood, is by no means limited thereto, but may be advantageously employed in other fields and for other uses where it is desired to generate and utilize electrical oscillatory energy. The reference to diathermy machines is by way of example and convenience of explanation.

In apparatus of the type herein considered, it is desirable to have available high frequency power at two or more frequencies. In the diathermy field, wave lengths varying from about 6 meters to 30 meters or more may be employed, these lying in the so-called ultra-short wave zone, and relatively large amounts of power may be desired, 500 Watts being considered a relatively large power in such field.

In the past, the desire for controllability of the frequency to be produced at any given time has reduced the relative efliciency and/or increased the cost of the apparatus.

Because of the relatively high currents, voltages and frequencies at which the apparatus works, the switching mechanism employed for controlling the frequency must be relatively large and rugged, of low resistance and with large and self-wiping contact areas. Such large and heavy switches are expensive in themselves, and their employment further increases the cost of other parts of the apparatus and reduces its. efficiency.

As an example, the space occupied by the apparatus is increased, and longer leads must be employed between component parts. This, in turn,increases the capacity of the apparatus and serves to increase the losses and thus to decrease the relative efficiency, as well as to increase its expense, and in general it may be stated in any case where it is desired to generate a plurality of ultra-high frequencies and to draw any considerable amount of power at such frequencies, selectively, from the generator, the cost is considerably increased and the efficiency consider- 50 ably decreased relative to that of a machine supplying only a single frequency.

It is an object of this invention to provide an oscillation generating system of the class described which will supply high-frequency power at a plurality of frequencies, and which is free 1936, Serial No. 105,476

from the disadvantages and shortcomings of the machines heretofore used for the purpose.

It is a further object of this invention to provide a system of the class described, in which frequency controlling switches are eliminated, or 5 if employed are small and inexpensive and do not substantially reduce the efficiency.

It is a further object of this invention to provide a system of the class described in which the act of connecting into the output circuit the particular output element to be employed automatically causes the frequency of oscillation generated to adjust itself to the value desired for such element, without any separate frequency selecting action by the operator. 5

It is still a further object of this invention to provide apparatus which will function satisfactorily at a high frequency with either parallel or series tuned output circuit, or at a lower frequency, without expensive or bulky switching mechanism, and with a minimum of apparatus.

It is still a further object of this invention to provide a system of the class described which will generate high frequency power on a plurality of frequencies simultaneously.

It is still a further object of my invention to provide a system in which a plurality of tubes may be employed for oscillation selectively either as a balanced oscillator, or with the tubes in parallel, without any change in circuit connections.

It is still a further object of this invention to provide such a system which may be energized from a commercial power line, and in which the filament and plate voltages may be simultaneously regulated to the optimum value for various power loads by a single control.

Still other objects and advantages will be apparent from the following specification.

The features of novelty which I believe to be characteristic of my invention are particularly pointed out in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, is described in the specification and illustrated in the accompanying drawings, in which- Figure 1 is a circuit diagram of one form of circuit embodying my invention,

Fig. 2 is a similar diagram of a modified form of apparatus embodying my invention, and

Fig. 3 is a similar diagram of still another form of my invention.

In accordance with the principles of my invention I employ a generating system for producing oscillations, which system may and pref- 55 erably does comprise a pair of vacuum tubes connected by a first oscillation or feed-back circuit as a balanced, or as it is sometimes called, push-pull or push-push system, the constants of which are so chosen that when such system is controlling, the system oscillates at its highest frequency.

In addition, I provide a second oscillation circuit connecting said tubes for oscillation in parallel, preferably at a lower frequency, and this second circuit is connected and arranged in such a manner that it is not necessary to disconnect or interrupt the frequency-determining elements of the first circuit in order to cause the system to oscillate at its second frequency.

Preferably, although not necessarily, the second circuit is left incomplete and arranged to be completed by the output or load element which is to draw current at the second frequency, and the circuit constants are so chosen that when the second circuit is completed, the system will oscillate at its second frequency, even though the first circuit is still connected and uninterrupted. Alternatively, however, the circuit constants may be adjusted so that when both oscillation circuits are complete, the system will generate oscillations of both frequencies simultaneously, or of either, depending on the load being drawn.

Referring now more particularly to Fig. 1, I and 2 designate a pair of vacuum tubes having respectively cathodes 3 and 6, control electrodes 4 and 1, and anodes 5 and 8. For simplicity I prefer to employ, and have shown, triodes with filamentary cathodes, but it will be understood that other tubes may be employed, if desired. The filamentary cathodes 3 and 6 may be connected together for parallel operation, as shown, or otherwise.

Connecting the tubes l and 2 for oscillation at a first frequency there may be provided plate coils 9 and Ill and grid coil II, the latter having its ends connected to grids l and l and its midpoint connected through resistance l2 to the cathode circuit.

Plate voltage may be supplied from secondary 28 of the step-up plate transformer through radio frequency choke 24, and the filament voltage may be supplied from secondary 26 of the step-down filament transformer later to be described. Resistor l2 connected between the cathodes and the mid-point of coil ll serves as a self-biasing resistor for the grid-filament circuit. It will be noted that no rectifier and filter need be employed, alternating current being applied to the plates.

The inductance and distributed capacity of coils 9, it and H are so chosen, together with the interelectrode capacities of the tubes as to constitute what may be regarded as a tunedgrid, tuned-plate balanced oscillation system (sometimes called push-pull) oscillating at the highest frequency desired.

A second oscillation circuit may also be provided, being formed by condensers l3 and M connected in series between the junction of coils s and if! and the cathode end of resistor l2, and condenser l5, connected from condenser is to the grid end of resistor l2, together with an inductance, such as the inductance cable customarily used in high-frequency diathermy machines connected between output terminals 22 and 23, and condenser 16, said cable being herein shown in dotted lines between terminals 22 and 23.

The values of the various elements of the circuit are preferably so chosen that the frequency of the system, when the tubes are operating in parallel, is somewhat lower than the frequency when the tubes are operating in the balanced system. Excellent results have been obtained when the system oscillates as a balanced oscillator at a wave length of 6 meters and in parallel at an average wave length of 28 meters. That is, when used as a diathermy machine with an inductance cable output, the inductance of the oscillation system with the tubes oscillating in parallel, will depend upon the disposition and arrangement of the inductance cable, and the second frequency will accordingly be raised or lowered somewhat, depending on the configuration of the cable.

It will also be noted that the second, or lower frequency oscillation circuit, is not completed until the inductance cable is connected between terminals 22 and 23. If the constants be properly chosen, when the starting switch 35 is closed, the system will oscillate as a balanced oscillator at the frequency determined by the constants of the balanced oscillation circuit, (in this case 6 meters) so long as the output cable is not connected to terminals 22 and 23. When the cable is so connected, the system will immediately shift into oscillation with the tubes in parallel, at the lower frequency determined by the constants of the second oscillation circuit, and, upon disconnection of the inductance cable, will shift back automatically to balanced (push-pull) operation at the higher frequency.

Should an attempt be made to withdraw an abnormally large amount of power from the inductance cable, this will be reflected as excessive damping of the system in this mode, and the system will periodically shift to balanced oscillation and return to parallel operation, this being evidenced by downward flickering of the plate current meter M. Further increase in load will cause the system to shift to balanced operation and to remain in such operation until the excessive load for parallel operation is removed, when it will return to parallel operation. Thus automatic overload protection is afforded for the parallel system without the use of circuit breakers, relays, fuses, or the like.

In case it is desired to have the system generate oscillations of both higher and lower frequencies simultaneously, oscillating in both modes at the same time, this may be accomplished by reducing the feed-back excitation of the lower frequency oscillation circuit, and increasing the feed back at the higher frequency. This adjustment may be fairly critical.

In Fig. 1, I have shown a parallel-tuned output or pick-up circuit for the higher frequency, which may be formed by pick-up coil I! tuned by a double condenser having similar sections l8 and I9 (each comprising stator and rotor) connected in series, both sections being simultaneously variable in the same sense, and the voltage across said sections being supplied to output terminals 28 and 2!, to which condenser electrodes may be applied, as shown in dotted lines. This connection is termed voltage feed.

In order to regulate the power output, a first control may be provided by adjustment of the plate voltage, it being understood that an increase in the plate voltage increases the power output. For optimum life of the tubes, it is desirable that the filament voltage be slightly increased with increase in plate voltage. This may be simply and effectively accomplished by the circuit of Fig. 1. It will be noted that terminals 33 and 34 are provided for connection to a commercial source of alternating current. The circuit includes line switch 35, fuse 36, and the primary winding 25 of the filament transformer. At one end of said primary winding 25 there may be provided a plurality of taps 32 32 32, over which switch 3|, connected to one side of the line, may be selectively operated to compensate for variations in line voltage.

The primary 27 of the plate transformer may be connected at one end to the terminal 32*, and at the other end of primary 25 there may be provided a plurality of taps 30 30 30 30 and 30 and off-contact 30, to be selectively engaged by switch 29, to which the other end of primary 2'! is connected.

The operation of this feature is as follows: The primary winding 25 acts as an auto-transformer, and adjustment of switch 29 increases or decreases the voltage across winding 21, by increasing or decreasing the portion of winding 25 across which 2'! is connected, thereby increasing or decreasing the voltage delivered by secondary 28. At the same time, it will be noted that as switch 29 is moved further clockwise, reducing the voltage delivered by winding 28, the current drawn by winding 27 traverses an increasing portion of winding 25, and this produces a drop in the voltage delivered by winding 25, thus simultaneously varying both the plate and filament voltage.

Referring now to Fig. 2, I have shown a modified form of my invention, which embodies the same principles of Fig. 1. In this figure, like reference numbers indicate like parts as in Fig. 1. As before, tubes and 2 are connected through plate coils 9 and I and grid coil I to form abalanced oscillator generating the highest frequency oscillations.

A second, and lower frequency, oscillation circuit, in which the tubes oscillate in parallel, is formed by coil 42, having one end connected to the midpoint between coils 9 and I0 and its other end connected through condenser 44 and switch 46 to the mid-point of coil The output at high frequency may be picked up by pick-up coils 40 and 4| shunted by double condenser l8, l9, connected to terminals 20 and 2|. The output at lower frequency may be picked up by pick-up coil 43, having one terminal connected to the mid-point between coils 40 and 4|, and its other terminal connected to output terminal 22.

Plate voltage may be supplied from transformer 48 through meter M, and resistor 45. By-pass condenser 41 may be provided across the secondary of transformer 48. For simplicity, the fila ment transformer and its connections are omitted, but it will be understood that any desired arrangement may be employed for supplying plate and filament current, including that shown and described in Fig. 1.

It will be noted that in this modification the second oscillation circuit is incomplete when switch 46 is open, but this switch, being in the grid lead, is traversed by minimum current, and does not need to be of the size and low resistance which would be necessary if it were in a part of the circuit carrying heavy current.

As before, the system is preferably so adjusted that when the second oscillation circuit is open, the system oscillates as a balanced system at high frequency, and when the second circuit is completed, by closure of switch 48, the tubes oscillate in parallel at a lower frequency.

The system of this figure differs from that of Fig. 1 in that the second oscillation circuit may be complete within the apparatus itself, the output circuit when connected to terminals 22 and 23, being not a part of the feed-back circuit, but being a part of the pick-up circuit.

When output electrodes are connected to terminals 20 and 2|, coils 40 and 4| and condenser sections I8 and I9 form a parallel tuned circuit with the condenser sections in series.

When output electrodes are connected to terminals 22 and 23, for lower frequency output, there is formed a series tuned circuit, from terminal 22, through coil 43, thence through coils 40 and 4| in parallel and through condenser sections l8 and E9 in parallel, to terminal 23. At this frequency, it will be understood, the inductance of coils 45 and 4| is negligible, and by reason of the parallel feed through condenser sections l8 and I9, four times the capacity is available for tuning which is available with the sections in series.

Referring now more particularly to Fig. 3, the modification therein shown is substantially the same as in Fig. 2, with the exception of the output circuits, which are somewhat modified to provide greater flexibility. As in Fig. 2, the tubes are connected through a first oscillation circuit forming a tuned-grid tuned-plate balanced oscillator, and through a second oscillation circuit with the tubes oscillating in parallel.

In this instance, I have shown five output terminals, 5|, 52, 53, 54 and 55 with switch 55 connected between terminals 5| and 54, and lower frequency pick-up coil 55 connected from the mid-point of double condenser l8, l9 to terminal 55, pick-up coil 40 being connected between terminals 5| and 52, and pick-up coil 4| between terminals 53 and 54.

In this modification, with condenser electrodes connected toterminals 5| and 54, and switch 56 open, it will be seen that the pick-up circuit is series tuned to the highest frequency, with condenser sections l8 and I9 in series.

With condenser electrodes on terminals 52 and 53, and switch 56 closed, the pick-up circuit is parallel tuned to the highest frequency, with the condenser sections I8 and H3 in series.

With condenser electrodes connected between terminal 55 and any other terminal, and switch 55 open, the pick-up circuit in series tuned to the lower frequency, using only one of the condenser sections, and with switch 56 closed, series tuned with both condenser sections in parallel.

For simplicity, both plate and filament supply also have been omitted in Fig. 3.

While I have shown and described certain forms of oscillation circuits, it should be understood that this is by way of example and not in limitation and that other types of oscillation circuits may be employed.

In these circuits, particularly in balanced operation at the higher frequency, satisfactory performance particularly, as regards balanced load distribution between the tubes, depends largely, if not entirely, upon the electrical symmetry of the circuit with respect to the center or neutral plane of the circuit layout. This plane of zero radio frequency potential is the plane midway between the tubes and at right angles to the plane of the tube axes. The layout of coils, panel parts and wiring cables should provide the greatest practical physical symmetry.

To minimize pro-loading at the highest frequency, all massive parts should be placed so as to be bisected by the neutral plane, and closed loops in the low frequency wiring should be avoided.

To minimize unbalancing reactions on the higher frequency circuit due to dissymmetries in the application of condenser pads to the patient, capacity feed from the plate coil to the pickup circuit should be minimized. Where substantial capacity feed is unavoidable, the high frequency pick-up coil or coils should be so poled with respect to the direction of winding of the plate coil that the magnetic and capacity feeds are aiding. The coupling between the high frequency pick-up coil and the plate coil should be adjusted to the lowest value that will allow normal loading.

The plate and filament control affords a first control of the amount of power supplied to the load. A second, and finer control, is afforded by the tuning condenser l8l9 in the pick-up circuit. Since this circuit is not the frequency setting circuit for the oscillator, its tuning may be varied without materially changing the frequency of the oscillations generated, and varying the tuning varies the impedance in the path to the load, and controls the amount of power delivered. This control allows very fine adjustments.

While I have shown and described certain preferred embodiments of my invention, it should be understood that modifications and changes may be made without departing from the spirit and scope of my invention, as will be clear to those skilled in the art.

I claim:

1. In an oscillation generating system, in combination, a vacuum tube oscillating system requiring plate and filament excitation, terminals for connection to a source of alternating current for providing said excitation, a transformer connected to said terminals for receiving current from said source and supplying filament current at a lower voltage, a second transformer for supplying plate current at a higher voltage, said second transformer having its primary connected across a. portion of the primary of the first transformer, and means for selectively changing the points of connection of said transformer to said rst transformer, whereby both plate and filament voltage may be simultaneously varied together for output control.

2. In an oscillation generating system, in combination, a vacuum tube oscillation system requiring plate and filament excitation, terminals for connection to a source of alternating current for providing said excitation, a transformer connected to said terminals for receiving current from said source and supplying filament current at a lower voltage, said transformer having one terminal of its primary winding connected to one side of said source, and having variable taps at the other end of said primary to compensate for variations in line voltage, a second transformer having one terminal of its primary connected to an intermediate point on the primary of said first transformer, and having the other terminal of its primary connected to a variable point on the primary of the second transformer, such that the number of primary turns across which said sec- Ondary is connected is variable, whereby adjustment of said variable point simultaneously increases the plate and filament excitation.

3. In a diathermy machine for supplying alternating current energy selectively through a series or parallel tuned pick-up circuit to condenser electrodes at a first frequency, and to a cable at a second frequency, in combination, an oscillation generating system, a plurality of pickup coils associated therewith and connected to a plurality of output terminals, a condenser connected to said pick-up coils, and switching means for connecting together a plurality of said output terminals, whereby a plurality of said pickup coils and said condenser form selectively a high frequency series-tuned ircuit, a high frequency parallel-tuned circuit tuned to the same frequency, and a series-tuned circuit tuned to a lower frequency.

4. In a diathermy machine for supplying alternating current energy selectively through a series or parallel tuned pick-up circuit to condenser electrodes at a first frequency, and to a cable at a second frequency, in combination, an oscillation generating system, a plurality of pickup coils associated therewith and connected to a plurality of output terminals, a condenser connected to said pick-up coils, and switching means for connecting together a plurality of said output terminals, whereby a. plurality of said pick-up coils and said condenser form selectively a high frequency series-tuned circuit, and a high frequency parallel-tuned circuit tuned to the same frequency.

5. In a diathermy machine for supplying alternating current energy selectively through a series or parallel tuned pick-up circuit to condenser electrodes at a first frequency and to condenser electrodes at a second and lower frequency, in combination, an oscillation generating system, a plurality of pick-up coils associated therewith and connected to a plurality of output terminals, a condenser having two sections connected to said pick-up coils, and switching means for connecting together a plurality of said output terminals, to form selectively, a high frequency series-tuned circuit with said condenser sections in series, a parallel-tuned circuit at the same frequency with said sections in series, and a lower frequency series-tuned circuit with either of said sections, or both, in parallel,

6. In an oscillation generating system, in combination, a pair of vacuum tubes each having an anode and a control electrode, a first oscillation circuit connecting said tubes for oscillation at a first frequency in push-pull mode, and a second oscillation circuit connecting said tubes for oscillation at a second and lower frequency in a parallel mode, the oscillation excitation of said tubes through said second circuit being relatively less than the excitation through said first circuit, whereby said tubes will oscillate at both frequencies and in both modes simultaneously.

'7. In a diathermy machine for supplying alternating current energy selectively through a series or parallel tuned pick-up circuit to output electrodes, in combination, an oscillation generating system, a plurality of pick-up coils associated therewith, a plurality of output terminals, double condenser connected to one of said pickup coils to form a closed tuned pick-up circuit, connections from said closed tuned circuit to a pair of said output terminals, a connection from a third output terminal to an intermediate point of said double condenser and a connection from a fourth output terminal through a second pickup coil to said first pick-up coil.

8. In an oscillation generating system for supplying alternating current energy at a plurality of frequencies, in combination, means for generating oscillations of the desired frequencies,

pick-up coils associated with said generating means, a plurality of output terminals associated with said pick-up coils and a double variable condenser connected with said pick-up coils and forming a closed tuned circuit supplying higher frequency currents to a pair of said output terminals, connections from another of said output terminals to the intermediate point of said double condenser to supply oscillations of a lower frequency and connections from a fourth output terminal to a point on said closed tuned circuit.

9. In a diathermy machine, in combination, a pair of vacuum tubes, each having an anode, a

cathode, and a control electrode, an inductance having opposite terminals connected to said control electrodes respectively, a second inductance having opposite terminals connected to said anodes respectively, a circuit for capacitatively applying energy of a first frequency to a load, said circuit being coupled to said second inductance, means comprising an inductance parallel tuned to a lower frequency connected between intermediate points on said first and second inductances, whereby said lower frequency is produced, and means for open-circuiting the connection of said last mentioned means for shifting the frequency from said lower frequency to said first frequency.

10. In a diathermy machine,'in combination, a pair of vacuum tubes each having an anode, a cathode and a control electrode, an inductance having opposite terminals connected to said control electrodes respectively, a second inductance having opposite terminals connected to said anodes respectively, a circuit for capacitatively applying energy of a first frequency to a load, said circuit being coupled to said second inductance, means comprising an inductance parallel tuned to a lower frequency connected between intermediate points on said first and second inductanoes, whereby said lower frequency is produced, said last mentioned inductance being an induction cable for inductively applying said lower frequency energy to a load, and means for opencircuiting the connection of said last mentioned means for shifting the frequency from said lower frequency to said first frequency.

ALEXANDER SENAU'KE. 

